U.S. patent application number 13/070967 was filed with the patent office on 2011-09-29 for integrated system for vapor generation and thin film deposition.
This patent application is currently assigned to MSP Corporation. Invention is credited to Thuc Dinh, Benjamin Y.H. Liu, Yamin Ma.
Application Number | 20110232588 13/070967 |
Document ID | / |
Family ID | 44654909 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110232588 |
Kind Code |
A1 |
Liu; Benjamin Y.H. ; et
al. |
September 29, 2011 |
Integrated system for vapor generation and thin film deposition
Abstract
An apparatus and method for generating vapor from a liquid
precursor for a thin film deposition on a substrate includes an
inlet section in fluid communication with a downstream vaporization
chamber section. The inlet section comprises a gas inlet for
receiving gas from a gas source through a gas flow sensor and a gas
flow control valve and a liquid inlet for receiving liquid from a
liquid source through a liquid flow sensor and a liquid flow
control valve. An electronic controller controls the gas and liquid
flow control valves thereby controlling the rates of gas and liquid
flow into the inlet section to generate vapor in the downstream
vaporization chamber section for thin film deposition on the
substrate.
Inventors: |
Liu; Benjamin Y.H.; (North
Oaks, MN) ; Ma; Yamin; (Roseville, MN) ; Dinh;
Thuc; (Shakopee, MN) |
Assignee: |
MSP Corporation
Shoreview
MN
|
Family ID: |
44654909 |
Appl. No.: |
13/070967 |
Filed: |
March 24, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61317728 |
Mar 26, 2010 |
|
|
|
Current U.S.
Class: |
122/451R ; 137/1;
137/487.5; 137/561R; 251/129.01 |
Current CPC
Class: |
Y10T 137/7761 20150401;
Y10T 137/0318 20150401; F01K 17/04 20130101; Y10T 137/0379
20150401; Y10T 137/8593 20150401 |
Class at
Publication: |
122/451.R ;
251/129.01; 137/561.R; 137/487.5; 137/1 |
International
Class: |
F22D 5/26 20060101
F22D005/26; F16K 31/02 20060101 F16K031/02; F15D 1/00 20060101
F15D001/00 |
Claims
1. An apparatus for generating vapor from a liquid precursor for
thin film deposition on a substrate including an inlet section in
fluid communication with a heated downstream vaporization chamber
section, the apparatus comprising: said inlet section comprising a
gas inlet for receiving gas from a gas source through a gas flow
sensor and a gas flow control valve and a liquid inlet for
receiving liquid from a liquid source through a liquid flow sensor
and a liquid flow control valve; and an electronic controller for
controlling the gas and liquid flow control valves thereby
controlling the rates of gas and liquid flow into said inlet
section to generate vapor in said heated downstream vaporization
chamber section for thin film deposition on the substrate.
2. The apparatus of claim 1 said gas flow sensor comprises a
thermal mass flow sensor or a Coriolis-force mass flow sensor.
3. The apparatus of claim 1 including a gas flow sensor comprised
of an orifice in said inlet section for the gas to flow through
causing the gas pressure upstream of said orifice to increase and a
pressure sensor to sense the resulting gas pressure upstream of
said orifice.
4. The apparatus of claim 3 including a temperature sensor to sense
the gas temperature for temperature compensation and mass flow
determination.
5. The apparatus of claim 1 said liquid flow sensor comprising a
thermal mass flow sensor or a Coriolis-force mass flow sensor.
6. The apparatus of claim 1 said liquid flow sensor comprising a
thermal mass flow sensor with a stainless steel sensing tube.
7. The apparatus of claim 1 said liquid flow sensor comprising a
thermal mass flow sensor with a sensing tube made of a non-porous,
electrically insulating material.
8. The apparatus of claim 7 said material comprising glass, quartz
or sapphire.
9. The apparatus of claim 1 and farther comprising a pressure
controller for controlling the gas pressure in said liquid
source.
10. The apparatus of claim 3, said orifice being capable of
atomizing the liquid flowing into said liquid inlet to form
droplets when gas flows through said orifice.
11. The apparatus of claim 3, said orifice be capable of causing
upstream gas pressure to be at least equal to the critical gas
pressure for creating sonic gas flow in said orifice.
12. An apparatus for generating vapor from a liquid precursor for
thin film deposition on a substrate including an inlet section in
fluid communication with a heated vaporization chamber section
located downstream, the apparatus comprising: said inlet section
having a gas inlet for receiving gas from a gas source through a
gas flow sensor; a liquid inlet for receiving liquid from a liquid
source through a liquid flow sensor; said liquid flow sensor having
a response time of less than about 250 milliseconds; and mechanisms
to control the rates of gas and liquid flow through said sensors to
generate vapor for thin film deposition on a substrate.
13. The apparatus of claim 12 said liquid flow sensor comprising a
thermal mass flow sensor with a sensing tube made of glass quartz
or sapphire.
14. The apparatus of claim 13 said liquid being sensed is a
precursor liquid containing an atomic species with an atomic number
of at least about 22.
15. An apparatus for generating vapor from a liquid precursor for
thin film deposition on a substrate, the apparatus comprising: an
atomizer with a gas inlet for receiving gas from a gas source
through a gas flow sensor and a gas flow control valve and a liquid
inlet for receiving liquid from a liquid source through a liquid
flow sensor and a liquid flow control valve and an orifice to
increase the gas velocity to atomize the liquid flowing through
said liquid inlet to form droplets; a heated vaporization chamber
to heat the gas and vaporize the liquid droplets to form vapor; and
said liquid flow control valve being separated from said liquid
flow sensor by a length of connecting tubing and located downstream
of said liquid flow sensor for controlling the rates of gas and
liquid flow into said atomizer to generate vapor for thin film
deposition on the substrate.
16. The apparatus of claim 15 said liquid control valve being (a)
mounted directly on the atomizer with no connecting tubing in
between, or (b) connected to said gas inlet by a length of tubing
shorter than about 30 cm or having an internal volume of less than
about 500 microliters.
17. The apparatus of claim 15, said liquid flow control valve
comprising a solenoid valve or a valve with a piezoelectric
actuator.
18. A multi-channel gas flow controller having a plurality of gas
flow channels, the controller comprising a metal block with
internal gas flow passageways and inlet and outlet ports for the
gas to flow through each gas flow channel being provided with an
orifice, a pressure sensor and a flow control valve; and a
multi-channel electronic controller for controlling the rate of gas
flow through each gas flow channel by providing a signal to the gas
flow control valve in response to an output signal from said
pressure sensor.
19. The apparatus of claim 18 including a temperature sensor for
sensing gas temperature to compensate for the effect of temperature
on a measured mass rate of gas flow.
20. The apparatus of claim 18 for providing gas flow control of at
least two gas flow channels.
21. A method of controlling the rate of gas and liquid flow into a
vaporization apparatus including an atomizer and a vaporization
chamber, said rate of gas flow being measured by a gas flow sensor
and controlled by a gas flow control valve, said rate of liquid
flow being measured by a liquid flow sensor and controlled by a
liquid flow control valve, said rates of gas and liquid flows being
controlled by an electronic controller to control said gas and
liquid flow rates to gas and liquid flow rate set point values.
22. A method for multi-channel gas flow control of an apparatus
comprising at least two flow channels, including sensing gas
pressure upstream of an orifice in each flow channel, and
controlling the rate of gas flow in each flow channel by an
electronic controller to control the rate of gas flow through each
flow channel in response to the gas pressure upstream of said
orifice.
23. The method of claim 21 including additionally measuring the
temperature of said gas to provide temperature compensation for
measuring the gas flow in mass flow units.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is based on and claims the benefit
of U.S. provisional patent application Ser. No. 61/317,728, filed
Mar. 26, 2010, the content of which is hereby incorporated by
reference in its entirety.
FIELD
[0002] This disclosure relates to a method and an apparatus for
generating vapor for thin film deposition on a substrate. The
substrates of interest include a semiconductor wafer for
fabricating integrated circuit devices such as microprocessors,
memory chips, as well as digital and analog circuitry for signal
processing, conditioning and/or data storage. The system is aimed
at reducing the cost of the vapor generating apparatus while
enhancing its performance and improving the productivity of the
deposition process and the through-put of the deposition tool.
BACKGROUND
[0003] Thin film deposition for semiconductor device fabrication is
generally carried out with one or more liquid precursor chemicals.
The liquid must be vaporized to form vapor in order to deposit thin
films by a vapor phase process such as chemical vapor deposition,
atomic layer deposition, plasma-enhanced chemical vapor deposition,
and other processes. Ideally, the vapor can be generated on demand
with little or no time delay. Limitation in the response time of
the traditional vapor generating equipment has led to a slow
buildup in vapor concentration and a delay in the startup of the
deposition process. This delay in startup has led to wasted time,
lost productivity and through-put of the deposition tool. While
these losses have been accepted as necessary, their elimination can
lead to a significant improvement in the efficiency and
productivity of the manufacturing fab. One objective of this
disclosure is to shorten the response time of the vapor generating
equipment in order to increase the through-put of the film
deposition tool.
[0004] Another aspect of the present disclosure is an integrated
approach to system design to simplify the vapor generation systems
so that the resulting apparatus is simpler, smaller and the
manufacturing cost is lower while the system performance is
enhanced.
SUMMARY
[0005] This disclosure describes an apparatus for generating vapor
from a liquid precursor for thin film deposition on a substrate.
The apparatus includes an inlet section in fluid communication with
a heated downstream vaporization chamber. The inlet section
comprises a gas inlet for receiving gas from a gas source through a
gas flow sensor and a gas flow control valve and a liquid inlet for
receiving liquid from a liquid source through a liquid flow sensor
and a liquid flow control valve. An electronic controller controls
the gas and liquid flow control valve thereby controlling the rate
of gas and liquid flow into the inlet section to generate vapor in
the heated downstream vaporization chamber section for thin film
deposition on a substrate.
[0006] This disclosure also describes an apparatus for generating
vapor from a liquid precursor for thin film deposition on a
substrate wherein the apparatus includes an inlet section in fluid
communication with a heated vaporization chamber section located
downstream. The inlet section has a gas inlet for receiving gas
from the gas source through a gas flow sensor, a liquid inlet for
receiving liquid form a liquid source through a liquid flow sensor,
the liquid flow sensor having a response time of no more than 250
milliseconds, and mechanisms to control the rate of gas and liquid
flow through the sensors to generate vapor for thin film deposition
on the substrate.
[0007] This disclosure also describes an apparatus for generating
vapor from a liquid precursor for thin film deposition on a
substrate. The apparatus comprises an atomizer with a gas inlet for
receiving gas from the gas source through a gas flow sensor and a
gas flow control valve, and a liquid inlet for receiving liquid
from a liquid source through a liquid flow sensor and a liquid flow
control valve, and an orifice to increase the gas velocity to
atomize the liquid flowing through the liquid inlet to form
droplets. A heated vaporization chamber heats the gas and vaporizes
the liquid droplets to form a vapor. The liquid flow control valve
is separated from the liquid flow sensor by a length of connecting
tubing to allow the liquid flow control valve to be located in
close proximity to the gas inlet of the atomizer thereby
controlling the rates of gas and liquid flow into the atomizer to
generate vapor for thin film deposition on the substrate.
[0008] This disclosure also describes a multi-channel gas flow
controller having a plurality of gas flow channels. The controller
comprises a metal block with internal gas flow passageways and
inlet and outlet ports for the gas to flow through. Each gas flow
channel is provided with an orifice, a pressure sensor and a flow
control valve. A multi-channel electronic controller for
controlling the rate of gas flow through each gas flow channel
provides a signal to the gas flow control valve in response to an
outlet signal from the pressure sensor.
[0009] This disclosure also describes a method of controlling the
rate of gas and liquid flow into a vaporization apparatus wherein
the apparatus includes an atomizer and a vaporization chamber. The
rate of gas flow is measured by a gas flow sensor and controlled by
a gas flow control valve, the rate of liquid flow being measured by
a liquid flow sensor and controlled by a liquid flow control valve.
The rates of gas and liquid flows are controlled by an electronic
controller to control the gas and liquid flow rate to gas and
liquid flow rate set point values.
[0010] This disclosure also includes a method for multi-channel gas
flow control of an apparatus comprising at least two flow channels.
The method includes sensing the gas pressure upstream of an orifice
in each flow channel, and controlling the rate of gas flow in each
flow channel by an electronic controller that controls the rate of
gas flow through each flow channel in response to the gas pressure
upstream of the orifice.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram of the integrated vapor
generation system for thin film deposition on a substrate
[0012] FIG. 2 shows the measured response of a commercially
available Coriolis-Force liquid flow controller (A), a thermal mass
flow control (B) and an experimental flow control system using a
glass-tube liquid flow sensor for increased response speed (C)
[0013] FIG. 3 is a schematic diagram of an integrated multi-channel
gas flow controller of this disclosure
DETAILED DESCRIPTION OF THE INVENTION
[0014] FIG. 1 is a schematic diagram of an integrated vapor
generation and delivery system in one embodiment. The major system
components are shown within the dotted rectangular area located
generally at 100. It includes an atomizer 110 mounted on a
vaporization chamber, 120, or connected to it through a
short-length of connecting tubing. The atomizer has an inlet 130
for a compressed gas to enter, an atomizing orifice, 140, for the
gas to flow through to form a high velocity gas jet to atomize the
liquid flowing through liquid inlet 150 to form a droplet spray.
The term orifice is used in its generic sense in this disclosure as
a flow restriction, whether or not it is in the form of an orifice,
a nozzle, a Venturi, or a flow constriction of some other
cross-sectional shape. The droplet spray is comprised of the
atomized liquid droplets suspended in the gas. The spray is
directed to flow into the heated vaporization chamber 120 to heat
the gas and vaporize the droplets. Heating is accomplished by an
electric heater and the chamber temperature is regulated with the
aid of a temperature sensor and a heater controller (not shown).
The resulting gas/vapor mixture then flows into the deposition
chamber, 160, for thin film deposition on a substrate. Deposition
chamber 160 is connected to a source of vacuum 170 to create the
proper vacuum for thin film deposition.
[0015] The compressed gas for atomizing the liquid to form droplets
for vaporization comes from a compressed gas source 180. The gas is
delivered to atomizer 110 at the desired rate of flow through a gas
flow control system comprised of a gas flow sensor 202, and a flow
control valve, 190. In the embodiment shown in FIG. 1, the flow
sensor 202 is comprised of the atomizing orifice 140, and pressure
sensor 200 located upstream of orifice 140 to sensing the upstream
gas pressure. For a specific rate of gas flow through the atomizing
orifice 140, the upstream gas pressure is a function of the gas
flow rate. The output of pressure sensor 200 can be used to measure
the rate of gas flow through the orifice. By means of control valve
190 the rate of gas flow can be adjusted or regulated to a specific
set-point value corresponding to the set-point gas flow rate
desired.
[0016] To achieve a high degree of accuracy in the measured rate of
gas flow, it is desired that the gas flow through orifice 140 be
equal to or higher than the critical pressure needed to maintain a
sonic gas flow velocity in the orifice. When the gas flow in the
orifice becomes sonic, the mass rate of flow through the orifice
becomes independent of the downstream gas pressure, the flow rate
being proportional to the absolute pressure of the gas upstream.
This pressure is sensed by pressure sensor 200. A temperature
sensor, 205, is placed in close thermal contact with the atomizer
110 to measure the temperature of the atomizer and the gas flowing
there-through. Knowing the temperature the measured rate of gas
flow can then be converted to standard mass flow rate units such as
standard liter per minute (slm), or standard cubic centimeter per
minute (seem). The standard conditions for mass flow measurement
are typically zero degree Celsius in temperature and one atmosphere
in gas pressure.
[0017] When the rate of gas flow through orifice 140 is below the
critical value, i.e. below the value needed to maintain sonic flow
through the orifice, the mass flow rate depends both on the
upstream gas pressure as well as the pressure downstream. In which
case an additional absolute pressure sensor or a differential
pressure sensor (both not shown) may be added for accurate mass
flow determination.
[0018] The above approach to gas flow sensing and measurement based
on measuring the pressure created by a gas flow rate through an
orifice is but one of several approaches that can be used. Another
approach is to use a thermal mass flow sensor in which the
convective cooling effect over a heated section of the tube is use
for flow sensing. Thermal mass flow sensors (U.S. Pat. Nos.
4,815,280, 4,977,916, 5,398,549, 5,792,592, 6,813,944, and
7,469,583) for gas flow measurement are among the most widely used
sensors for gas flow sensing and control in semiconductor thin film
deposition applications.
[0019] Yet another approach to gas flow sensing is the
Coriolis-force sensor (U.S. Pat. Nos. 6,513,392, and 6,526,839), in
which a U-shaped metal tube is driven to vibrate at its natural
oscillating frequency. When a gas flows through the vibrating
U-tube at a specific mass rate of flow, a torque will develop
causing the vibrating U-tube to become twisted. The degree of twist
is then measured optically or by means of an electro-mechanical
sensor to provide a signal for mass flow. Unlike the thermal mass
flow sensor which senses the mass flow by means of the thermal
effect produced by a flowing gas stream, the Coriolis-force sensor
responds directly to the mass flow rate, thereby making mass flow
measurement easier and potentially more accurate.
[0020] Any of the approaches described above to flow sensing, in
principle, can be used in the integrated vapor generation and
delivery system described in this disclosure, with factors such as
accuracy, reliability, and cost being the most important.
[0021] The valve for controlling the rate of gas flow through the
system, i.e. valve 190, can be a conventional solenoid valve, or a
piezoelectric valve. The former uses an electric solenoid to vary
the flow restriction to control the rate of gas flow, whereas the
latter uses a piezoelectric actuator to produce the needed valve
movement for gas flow control. The use of a solenoid valve or a
piezoelectric valve for flow adjustment and/or control is well
known to those skilled in the art of flow adjustment and control by
electro-mechanical means and will not be further discussed.
[0022] The integrated system of FIG. 1 for vapor generation and
delivery also includes a liquid flow sensor, 210, which provides an
electrical output in response to the rate of liquid flow through
the sensor. Sensor 210 is connected to a pressurized liquid source,
shown generally located at 220, and to liquid flow control valve
230, which in turn is connected to the liquid inlet 150 on atomizer
110. For clarity, the liquid flow control valve 230 is shown
connected to the atomizer liquid inlet through a short length of
tubing. In practice, it is preferable that the valve be mounted
directly on the atomizer to minimize the "liquid dead volume," the
volume of liquid residing in the liquid flow passageway downstream
of the valve from the internal point of liquid shut-off when the
valve is at its closed position to the point where the liquid flows
out the liquid flow passageway into the atomizer inlet 150. A small
liquid dead volume will increase the response speed of the vapor
generation system and reduce its response time.
[0023] The manner in which the rate of liquid flow is adjusted
and/or controlled is similar to that described in paragraphs [0012]
and [0013] for gas flow adjustment and control. Like valve 190 for
gas flow control, valve 230 for liquid flow control can also be a
solenoid actuated valve or a piezo-electric valve using a
piezoelectric actuator. For liquid flow control, a piezoelectric
actuator is preferred because of its short response time and the
higher accuracy in controlling the small mechanical movement needed
for precise liquid flow control.
[0024] The same principles used for gas flow sensing and described
in paragraphs [0012] and [0013] can also be used for sensing the
rate of liquid flow in a tube. Thermal liquid flow sensors and
Coriolis-force sensors are both available commercially and both
have been used for liquid flow sensing and control for vapor
generation in semiconductor device fabrication.
[0025] For liquid flow sensing in vapor-phase thin film deposition
processes in semiconductor device fabrication, the sensor tube is
typically made of metal, with stainless steel being the most common
material used. This is the case both for the thermal and the
Coriolis force sensors used for liquid flow sensing in
semiconductor application.
[0026] One disadvantage of using a stainless steel tube sensor for
liquid flow sensing is its relatively high density compared to
other potentially more advantageous sensing tube material. A tube
of a specific geometrical dimensions constructed of a high density
material such as stainless steel will have a large mass compared to
a tube constructed of a material with a lower density. The larger
mass of a stainless steel tube will give rise to a high thermal
inertia in the case of a thermal mass flow sensor, and a lower
vibrating frequency in the case of a Coriolis-force sensor. The
result is a slower response speed of the sensor. The response time
of the available metal tube liquid flow sensors is typically 500 ms
or more, with response time as long as several seconds being quite
common for some commercially available thermal mass flow
sensors.
[0027] To be acceptable for liquid flow sensing for vapor
generation in thin film deposition, the material must be inert,
i.e. does not react chemically with the precursor liquid to be
vaporized. It must also be non-porous, so that reactive gases in
the ambient atmosphere will not diffuse through the porous tube
walls to react with the reactive liquid chemical precursors flowing
inside. In addition, the material density of the tube should be low
to reduce thermal and mechanical inertia and increase the sensor
response speed. In the case of a thermal flow sensor, a material
with a high thermal conductivity is desired for good heat
conduction and increased sensitivity.
[0028] The density of stainless steel, which is an electrical
conductor, is about 8.0 g/cm.sup.3. In comparison, the density in
g/cm.sup.3 for some electrically insulating solids such as glass
(2.4-2.8), quartz (2.65) and sapphire (.about.6.5) are considerably
lower. The thermal conductivity in units of Btu/hr-ft-F is 19 for
stainless steel, 3.4-6.4 for quartz, and 19.7-20.2 for sapphire.
Because of their lower densities, these insulating solids when used
to fabricate a sensor tube for a thermal mass flow sensor or a
Coriolis-force flow sensor will give rise to a shorter response
time compared to that of stainless steel.
[0029] FIG. 2 compares the response time of an experimental
glass-tube liquid sensor compared to two conventional stainless
steel tube sensors. A response time less than 500 ms is easily
achievable for the glass tube sensor. In the laboratory a sensor
response as short as 10 ms has been measured with the glass-tube
sensor.
[0030] While stainless steel is generally accepted for thin film
deposition for semiconductor applications, precursor chemicals
containing atomic species such as hafnium, zirconium, ruthenium,
strontium, etc. are becoming increasingly more important in
semiconductor integrated circuit device fabrication. Some of these
newer precursor chemicals can react with trace metals in stainless
steel, such as nickel. Nickel is widely used as a catalyst in
industrial applications and is catalytically reactive with some
modern precursor chemicals. It can lead to chemical reaction with
the precursor liquid creating by-products that can clog the small
liquid flow passageways in the sensor tubes. This is especially
important for modern precursor chemicals containing atomic species
with atomic numbers larger than that of rubidium (atomic number 37)
or even those with atomic number larger than that of titanium
(atomic number 22). For these applications, a sensor tube made of
glass, quartz, or sapphire would be advantageous.
[0031] The integrated vapor generation system of FIG. 1 also
includes a pressure controller for pressurizing the liquid source.
The liquid source shown generally located at 220 provides the
liquid precursor chemical needed for vaporization and thin film
deposition. It includes a container 240, with an inlet, 250, for
compressed gas to enter and an outlet, 260, for the pressurized
liquid to flow out. Liquid is filled to level 270, so that space
280 above is filled with pressurized gas, which exerts the needed
gas pressure on the liquid 290 below to cause the liquid to become
pressurized. The compressed gas at the required pressure thus
provides the motive force needed to cause the liquid to flow from
source 220, through tube 265, liquid flow sensor 210, and control
valve 230 and into the atomizer 110 where the liquid is atomized to
generate vapor in the heated vaporization chamber 120.
[0032] The integrated vapor generation system of FIG. 1 also
provides a gas with the required regulated gas pressure for the
liquid source, 220. Pressure regulation is achieved by means of an
on/off valve 300 and pressure sensor, 310. When pressure sensor 310
senses a pressure below the set-point value, valve 300 will open to
allow the pressurized gas at the source pressure from gas source,
180, to flow into the liquid container, 240 to increase its
pressure, the pressure of the compressed gas in source 180 being
higher than the regulated gas pressure for liquid source 220. Upon
reaching the desired set-point value, valve 300 will close. An
auxiliary on/off valve, 320, referred to as a bleed valve, can be
opened to allow the gas in container 240 to flow out, thereby
reducing the gas pressure, if a lower pressure is needed in the
pressurized liquid container 240.
[0033] The integrated vapor generation system of FIG. 1 also
includes a vaporization system controller, 400, to provide the
overall control for the system. Output signals from the pressure,
temperature and flow sensors in the system are communicated to the
vaporization system controller through input lines, 410. Set-point
values for the controlled parameters are communicated from the
controller for the film deposition tool through lines 420 on the
vaporization system controller. Output signals from the
vaporization system controller are communicated to the control
valves for flow and pressure control through output lines, 430.
Communication between the tool controller and the vaporization
system controller 400 through lines 420 can be analog in nature, or
digital using one of the standard digital communication protocols
such as RS232, RS485, Ethernet, Devicenet, Modbus, etc.
The traditional approach to liquid flow control for vapor
generation is to use a liquid flow controller, in which the liquid
flow sensor 210 of FIG. 1 is combined with liquid flow control
valve 230 to form a single integrated liquid flow controller unit
with built-in electronic circuitry to sense the flow and control
the rate of liquid flow (U.S. Pat. No. 4,977,916, D436876). In this
traditional design the outlet of control valve 230 is connected by
a length of tubing to the atomizer inlet 150. The integrated vapor
generation system of FIG. 1 uses a liquid flow sensor 210 and a
liquid flow control valve 230 as separate independent units, which
can be connected by a length of connecting tubing in between so
that the flow sensor and the liquid flow control valve can be
located at the most appropriate position for each in order to
achieve the best overall system performance.
[0034] For liquid flow control, the pressure of liquid source 220
is typically in the range between 1 to 4 atmospheres or
approximately 760 to 3000 Torr. At the point where the liquid
enters the atomizer at inlet 150, which is located downstream of
the atomizing orifice, the liquid is exposed to a vacuum gas
pressure, at which point the liquid pressure may be in the range
between less 10 Ton to 100 Torr. A liquid in source 220 is in
contact with a gas at high pressure. This high pressure gas will
cause some gas to be absorbed into the liquid to form a dissolved
gas solution. When this liquid solution flows through flow control
valve 230 its pressure will drop by more than 300 fold in some
cases. This sudden drop in liquid pressure will cause the dissolved
gas to come out of the liquid solution and form gas bubbles. The
bubbles can grow to a large size if the tubing connecting flow
control valve 230 and inlet 150 on atomizer 100 is long. The flow
of liquid into atomizer 110 will thus be interrupted periodically
by gas bubbles formed in the liquid to cause the liquid flow into
the atomizer to become unsteady, thereby causing vapor output from
the vaporization system to fluctuate, leading to flow instability
in the tool and non-uniform film thickness on the wafer.
[0035] The above problem of liquid flow fluctuation due to bubble
formation in the liquid flow line can be greatly reduce or
eliminated by locating the liquid flow control valve directly on
the atomizer. Experiments in the laboratory have shown that by
relocating the liquid flow control valve from the liquid flow
controller in a traditional liquid flow control system to the new
design of FIG. 1 where the control valve is separated from the flow
sensor and mounted directly on the atomizer or connected to it by a
short length of tubing can greatly reduce or eliminate entirely the
fluctuating liquid flow caused by gas bubbles. In general, the
shorter is the length of the liquid flow pathway between the liquid
flow control valve and the atomizer gas inlet, the shorter will be
the residence time of liquid in this passageway, and better the
flow stability will be. To achieve the best performance, the length
of tubing generally should be shorter than about 30 cm or having an
internal volume of less than 500 microliters
[0036] FIG. 3 is a schematic diagram of an integrated multi-channel
gas flow control system to provide multi-channel gas flow control
for use in thin film deposition. For clarity only two flow channels
are shown. In principle, many more flow channels can be provided to
meet the need of a specific application. In practice, a specific
film deposition tool will need only a limited number of flow
control channels and the number of flow channels provided in a
given integrated multi-channel flow control system can be selected
to meet the actual need of a single film deposition tool.
[0037] The integrated multi-channel flow control system is shown
located at 500 in FIG. 3. In the schematic two-channel system shown
in FIG. 3, a metal block, 510, is provided with inlet and outlet
ports and internal gas flow passageways to direct the flow from a
compressed gas source, 650, to flow into the metal block through
inlet port 520, then through outlet ports, 540 and 545, into gas
flow control valves 570 and 575 respectively. The gas flow control
valves 570 and 575 are mounted on the sides of metal block 510 so
that the gas, after passing through valves 570 and 575 will be
returned to the metal block through ports 550 and 555. Upon
re-entering entering the metal block, the two separate gas streams
then flow through orifices 560 and 565 to create the gas pressure
needed for flow sensing. Pressure sensors 580 and 585 then sense
the respective gas pressure upstream of orifices 560 and 565 for
sensing the rate of gas flow through the orifices. A temperature
sensor 590 is placed in close thermal contact with metal block 510
to sense the temperature of the metal block and the temperature of
the gas flowing there-through for accurate temperature compensation
and mass flow measurements. Electronic controller 600 is provided
with the necessary input lines 610 to receive the output signal
from the pressure and temperature sensors as input signal to
controller 600. Like the electronic controller 400 in FIG. 1,
controller 600 is also provided with lines 420 for digital or
analog communication with the tool controller, and output lines 430
for controlling the rate of gas flow through the respective gas
flow control valves.
[0038] Controllers 400 and 600 are typically microprocessor-based
electronic controllers with internal memories for program and data
storage, circuitry to receive input signals in analog and digital
forms, provide output signals to carry out various control function
through electromechanical transducers, such as solenoid and
piezoelectric actuated valves. A single micro-processed based
controller can usually carry out a multitude of computation and
control functions making the use of such microprocessor based
controllers particularly advantageous for controlling the gas and
liquid flow rates, and additional control functions such as gas
pressure control, and temperature compensation for accurate gas
flow measurement. The capability of microprocessor based
controllers are well known to those skilled in the art of designing
such control systems and will not be further discussed in this
disclosure.
[0039] The above described approach to designing an integrated
vapor generation and delivery system including the design of a
multi-channel gas and liquid flow controller can lead to cost
savings by eliminating redundant system components. A single
controller can be used to control the myriads of controlled
functions in vapor generation for thin film deposition in
semiconductor device fabrication including control of flow of gas
and liquid flowing into the same atomizer. The result is an overall
system that is small and compact, with reduced cost of
manufacturing and improved performance characteristics such as
improved reliability and shortened response time.
[0040] The traditional approach to vaporization system design is to
use separate gas and liquid flow controllers each with its own
sensor, flow controller and an electronic controller, packaged into
stand-alone systems. Each flow controller has its own flow control
valve and flow sensor built into a common flow controller body that
needs to be machined individually, then assembled with the
electronic sensing and control circuitry for flow control. The
integrated system approach of the present disclosure, in the case
of the multi-channel gas flow control system, uses one single
mechanical base to house the separate flow channels. An 8-channel
system will thus have only one metal block for all eight channels,
and one microprocessor based controller to control the flow for all
eight flow channels, a single temperature sensor to sense the
temperature for all eight channels, etc. The impact of such an
approach is considerable in terms of size, cost saving, and
improved performance characteristics.
[0041] In addition to cost saving, reduced physical size, the
integrated system can also lead to improved reliability. In the
traditional approach, when separate components are used each with
its own controller, the components are connected by tubing
connections which must be leak-proof and vacuum tight. The overall
physical space occupied by the separate components and the
connecting tubing and fittings is considerably larger compared to
the integrated system described in this disclosure. The result is
that the integrated system of this disclosure is smaller and
occupies a smaller space. By eliminating unnecessary tubing
connections, the system also becomes more reliable in terms
potential leakage of ambient air into the vacuum system through
small leakage crevasses in the fittings and tubing welds. The end
result is a small compact system with a lower cost of manufacturing
and higher reliability in performance.
[0042] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
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